Showing papers on "Spin canting published in 2013"

Yafet–Kittel-type magnetic order in Zn-substituted cobalt ferrite nanoparticles with uniaxial anisotropy

Abstract: Zn-substituted cobalt ferrite (Zn x Co1−x Fe2O4 with 0.0 ≤ x ≤ 1.0) nanoparticles coated with triethylene glycol (TREG) were prepared by the hydrothermal technique. The effect of Zn substitution on temperature-dependent magnetic properties of the TREG-coated Zn x Co1−x Fe2O4 nanoparticles has been investigated in the temperature range of 10–400 K and in magnetic fields up to 9 T. The structural, morphological, and magnetic properties of TREG-coated Zn x Co1−x Fe2O4 NPs were examined using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The average crystallite size estimated from X-ray line profile fitting was found to be in the range of 7.0–10 nm. The lattice constant determined using the Nelson–Riley extrapolation method continuously increases with the increase in Zn2+ content, obeying Vegard’s law. TEM analysis revealed that the synthesized particles were nearly monodisperse, roughly spherical shaped nanoparticles in the size range of 9.0–15 nm. FT-IR spectra confirm that TREG is successfully coated on the surface of nanoparticles (NPs). The substitution of non-magnetic Zn2+ ions for magnetic Co2+ ions substantially changes the magnetic properties of the TREG-coated Zn x Co1−x Fe2O4 NPs. The saturation magnetization and the experimental magnetic moment are observed to initially increase (up to x = 0.2), which is explained by Neel’s collinear two-sublattice model, and then continuously decrease with further increase in Zn content x. This decrease obeys the three-sublattice model suggested by Yafet–Kittel (Y–K). While the Y–K angle is zero for the CoFe2O4 NPs coated with TREG, it increases gradually with increasing Zn concentrations and extrapolates to 82.36° for ZnFe2O4 NPs coated with TREG. The increase in spin canting angles (Y–K angles) suggests the existence of triangular (or canted) spin arrangements in all the samples (except for the samples with x = 0.0) under consideration in this work. From the computation of Y–K angles for the TREG-coated Zn x Co1−x Fe2O4 NPs, it can be concluded that all the zinc-doped cobalt ferrite nanoparticles (for x > 0.0) have a Y–K-type magnetic order, while the pure cobalt ferrite nanoparticles (x = 0.0) have a Neel-type magnetic order. Zero field cooled (ZFC) and field cooled (FC) measurement results further verify that the samples with 0.6 ≤ x ≤ 1.0 have superparamagnetic behavior at room temperature, which shows weak interaction between magnetic particles. The blocking temperatures obtained from ZFC–FC curves decrease as a function of Zn concentration. It was found that the effective magnetic anisotropy, the coercivity, and remanence magnetization continuously decrease with increasing Zn concentration. Lower reduced remanent magnetization (M r/M s) values (<0.5) suggest that all the samples have uniaxial anisotropy. Ferromagnetic resonance (FMR) measurement shows that the FMR spectra of all the samples have broad linewidth because of the magnetic nanoparticles with randomly distributed anisotropy axes, and the decrease in the internal field conversely leads to the increase in the resonance field with respect to increasing Zn concentration.

Facile sonochemical synthesis of high-moment magnetite (Fe 3 O 4 ) nanocube

Abstract: Monodisperse magnetite nanocubes with uniform particle size of about 80 nm have been synthesized in aqueous medium by single reaction sonochemical method using inexpensive and non-toxic metal salt (FeSO4·7H2O) as reactant. The crystallinity of the magnetite nanocube is enhanced by annealing treatment up to 600 °C with uniform shape and size distribution, after that a distortion in shape and a broad size distribution are obtained at 700 °C annealing temperature. The magnetic characterization of the nanoparticles reveals saturation magnetization of 91 emu/g at 5 K for as-synthesized sample and 94.8 emu/g for the sample which annealed at the temperature of 600 °C in a vacuum chamber. However, the saturation magnetization has been observed to decrease with further increase in annealing temperature and this has been attributed to the presence of a thin magnetic dead layer at the surface caused by shape anisotropy distortion and broken exchange bonds, and spin canting on the surface of the particles in addition to the formation of a small amount of maghemite phase.

Spin Structures in Magnetic Nanoparticles

Abstract: Spin structures in nanoparticles of ferrimagnetic materials may deviate locally in a nontrivial way from ideal collinear spin structures. For instance, magnetic frustration due to the reduced numbers of magnetic neighbors at the particle surface or around defects in the interior can lead to spin canting and hence a reduced magnetization. Moreover, relaxation between almost degenerate canted spin states can lead to anomalous temperature dependences of the magnetization at low temperatures. In ensembles of nanoparticles, interparticle exchange interactions can also result in spin reorientation. Here, we give a short review of anomalous spin structures in nanoparticles.

Triangle, square and delta-chain based cobalt tetrazolate magnets.

Abstract: Three novel tetrazole-based frustrated magnets, namely, Co3(OH)2(3-ptz)2(SO4)(H2O)4 (1), Co2(OH)(tzba)(H2O)4 (2) and [Co(OH)(tta)] (3) (3-ptz = 5-(3-pyridyl) tetrazole, H2tzba = 4-(1H-tetrazol-5-yl) benzoic acid, Htta = 1H-tetrazole) were hydrothermal synthesized and magnetically characterized. Compound 1 is a 2D (4,4) layered structure assembled by sulfate capped triangular [Co3(μ3-OH)(μ3-SO4)] clusters and in situ synthesized μ3-3-ptz ligands. Compound 2 features Co3(μ3-OH) triangle based magnetic Δ-chains linked with in situ generated μ5-tzba ligands to form a 2D layer. Compound 3 is a uninodal eight-connected body-centered-cubic (bcu) 3D network with square Co4O4 clusters as nodes and μ4-tta ligands as linkers. Interestingly, spin frustration was observed in these complexes due to inherent spin competition in triangle, Δ-chain and square. Magnetic studies show that 1 behaves as antiferromagnet, while 2 and 3 exhibits spin canting and long-range magnetic ordering.

Enhanced ferromagnetic moment in Co-doped BiFeO3 thin films studied by soft x-ray circular dichroism

Abstract: BiFeO3 (BFO) shows both ferroelectricity and magnetic ordering at room temperature, but its ferromagnetic component, which is due to spin canting, is negligible. Substitution of transition-metal atoms such as Co for Fe is known to enhance the ferromagnetic component in BFO. In order to reveal the origin of such magnetization enhancement, we performed soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD) studies of BiFe1−xCoxO3 (x = 0 to 0.30) (BFCO) thin films grown on LaAlO3(001) substrates. The XAS results indicated that the Fe and Co ions are in the Fe3+ and Co3+ states. The XMCD results showed that the Fe ions show ferromagnetism, while the Co ions are antiferromagnetic at room temperature. The XAS and XMCD measurements also revealed that part of the Fe3+ ions are tetrahedrally co-ordinated by oxygen ions but that the XMCD signals of the octahedrally coordinated Fe3+ ions increase with Co content. The results suggest that an impurity phase such as the ferrimagnetic...

Four coordination polymers based on identical eight-connected heptanuclear clusters: spin canting, spin glass, antiferromagnetism, and gas adsorption.

Abstract: Four 3D coordination polymers, [Co7(OH)4(H2O)2(ina)4(ip)3]·10H2O (1·10H2O, ina = isonicotinate, ip = isophthalate), [Ni7(OH)4(H2O)2(ina)4(ip)3]·10H2O (2·10H2O), [Co7(OH)4(H2O)2(ina)4(pip)3]·5H2O (3·5H2O, pip = 5-phenyl-isophthalate), and [Ni7(OH)4(H2O)2(ina)4(pip)3]·5H2O (4·5H2O), respectively, were hydrothermally synthesized. They crystallized in the orthorhombic space group Pba2 for 1·10H2O and 2·10H2O and monoclinic space group P2/n for 3·5H2O and 4·5H2O, respectively, and were constructed with the identical 8-connected heptanuclear {M7(OH)4} (M = Co(II) or Ni(II)) clusters, possessing uninodal hexagonal primitive net with the point symbol {3(6)·4(18)·5(3)·6}. The four coordination polymers showed dominant antiferromangetic properties, in which 1·10H2O shows spin-canted behavior and 2·10H2O exhibits the coexistence of spin canting and spin glass. Meanwhile, the activated polymers 1 and 2 possessed permanent porosity, displaying relatively large H2 uptake capacity (77 K, 1 atm) of 114 and 133 cm(3) g(-1), and CO2 uptake capacity (273 K, 1 atm) of 65.8 and 73.3 cm(3) g(-1), for 1 and 2, respectively.

Effect of Divalent Cation Substitution in the Magnetoplumbite Structured Bafe12o19 System

Abstract: Synthesis of magnetically ordered barium hexaferrite powders and the adjustment of magnetic properties for perpendicular magnetic recording media are realized through substitution of divalent cation (Ca) in the BaFe12O19 system. The Ca2+ substituted Ba1−xCaxFe12O19 (where x = 0.05, 0.1, 0.15 and 0.2) compounds have been prepared through solid state reaction technique. The powder X-ray diffraction analysis reveals that all the prepared compounds crystallized in magnetoplumbite hexagonal structure and the flat hexagonal platelet morphology of the crystallites was identified through scanning electron microscopy. The formation of magnetoplumbite structured Ba1−xCaxFe12O19 system due to mechanical activation was supported by micro-Raman measurements. Both pure and Ca substituted BaFe12O19 compounds exhibit sharp intense peaks which reveals defect free environment in the crystal lattice. From the room temperature magnetization studies, it was observed that the saturation magnetization (MS) and remanent magnetization (MR) values drastically decreases for the Ba0.95Ca0.05Fe12O19 compound which may be due to the existence of spin canting effect and leads to the reduction of super exchange fields. The increase in MS and MR values for the Ba0.9Ca0.1Fe12O19 and Ba0.85Ca0.15Fe12O19 compounds could be attributed to the enhanced hyperfine fields at 12k and 2b sites due to the strengthening of Fe3+–O–Fe3+ super exchange interactions. A large reduction in the coercivity value from 3,090 to 1,548 Gauss may be attributed to the fall in magneto crystalline anisotropy. The high temperature magnetization studies infer that while increasing substitution level of Ca in the BaFe12O19 system results in decreasing trend in Curie temperature. The room temperature dielectric measurement shows that the incorporation of Ca2+ in the BaFe12O19 system results with increase in the dielectric constant and this case substantiates the space charge polarization. The magnetically ordered BaFe particulate having higher saturation and low coercivity values with superior magnetic and dielectric behaviour exhibiting the possibility for future high-recording-density storage products.

Effects of holmium substitution on multiferroic properties in Tb0.67Ho0.33MnO3

Abstract: In this work, the structural, electrical, and magnetic properties of orthorhombic TbMnO3 and Tb0.67Ho0.33MnO3 ceramics are presented. The lattice parameters and the Mn-O-Mn bond angle were found to decrease with Ho-substitution as evidenced by Rietveld refinement of the X-ray diffraction data and Raman spectroscopy measurements. A weak ferromagnetic moment was observed in both dc and ac magnetic measurements of the Ho-substituted sample possibly due to spin canting in the antiferromagnetic phase. Tb0.67Ho0.33MnO3 was confirmed to be multiferroic with appearance of spontaneous polarization below 25 K and an additional increase in polarization ∼15.5 K associated with the ordering of the Ho3+ moments.

Substitution effects of La 3+ ions on the structural and magnetic properties of Co 2 Y hexaferrites synthesized by sol–gel autocombustion method

Abstract: Y-type hexaferrite Sr2Co2LaxFe12−xO22 (x = 0.0, 0.05, 0.10, 0.15, 0.20) powders have been synthesized using the sol–gel autocombustion method. Differential Scanning Calorimetry, Thermogravimetry, Fourier Transform Infra-Red spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometery were used to investigate the samples. XRD patterns confirm the formation of Y-type hexaferrite phase. SEM patterns show that mostly grains exhibit rod shape and some appear in the form of hexagonal platelet shape. The rod or rice shape hexaferrite may be used in catalysis, information storage, surface enhanced Raman scattering, imaging and sensing. The samples with hexagonal platelet-like shape particles may be suitable as microwave absorbing materials. The energy dispersive X-ray spectroscopy spectrum shows the presence of dissolved reactants Sr, Co, La and Fe. The saturation magnetization (Ms) calculated using the law of approach to saturation decrease with the increasing of lanthanum (La3+) contents. The decrease in ‘Ms’ may be because of magnetic dilution and spin canting and hence reduction in the super-exchange interactions. The retentivity (Mr) and coercivity (Hc) enhance with the increase of La3+ contents. The enhancement in coercivity from 193 to 598.6 Oe may be because of increase in the porosity of samples with the increase of La3+ contents. The coercivity of the synthesized materials is few hundred oersteds (Oe), which may be suitable for security, switching, sensing, high frequency applications and is also favorable for electromagnetic materials.

Nature of magnetic domains in an exchange coupled BiFeO3/CoFe heterostructure

Abstract: We use the micromagnetic model to simulate magnetization in a multidomain BiFeO3(BFO)/CoFe bilayer. We show that CoFe couples to weak ferromagnetism on the BFO surface and breaks into domains that correspond exactly with BFO domains. Switching the direction of the BFO spins switches the corresponding CoFe domains and reverses the net magnetization. Since magnetization is coupled to polarization in BFO, this demonstrates a mechanism for controlling magnetization reversal with an electric field. Comparison with experimental values of BFO surface moment and hysteresis allows us to extract BFO/CoFe exchange and spin canting energies and predict behavior for domains of varying sizes.

A two-dimensional oxamate- and oxalate-bridged Cu(II)Mn(II) motif: crystal structure and magnetic properties of (Bu4N)2[Mn2{Cu(opba)}2ox].

Abstract: A new compound of formula (Bu4N)2[Mn2{Cu(opba)}2ox] (1) [Bu4N(+) = tetra-n-butylammonium cation, H4opba = 1,2-phenylenebis(oxamic acid), and H2ox = oxalic acid] has been synthesized and magneto-structurally investigated. The reaction of manganese(II) acetate, [Cu(opba)](2-), and ox(2-) in dimethyl sulfoxide yielded single crystals of 1. The structure of 1 consists of heterobimetallic oxamato-bridged Cu(II)Mn(II) chains which are connected through bis-bidentate oxalate coordinated to the manganese(II) ions to afford anionic heterobimetallic layers of 6(3)-hcb net topology. The layers are interleaved by n-Bu4N(+) counterions. Each copper(II) ion in 1 is four-coordinate in a square planar environment defined by two amidate-nitrogen and two carboxylate-oxygen atoms from the two oxamate groups of the obpa ligand. The manganese(II) ion is six-coordinate in a somewhat distorted octahedral surrounding that is built by two oxalate-oxygen and four carbonyl-oxygen atoms from two [Cu(opba)](2-) units. The magnetic properties of 1 in the temperature range 1.9-300 K correspond to those expected for the coexistence of intralayer antiferromagnetic interactions of the type copper(II)-manganese(II) across oxamato and manganese(II)-manganese(II) through oxalato bridges plus a weak spin canting in the very low temperature domain. Simulation of the magnetic data through quantum Monte Carlo methodology reveals the magnitude of the intralayer magnetic interactions [J(CuMn) = -32.5(3) cm(-1), and J(MnMn) = -2.7(3) cm(-1)], their values being within the range of those previously observed in lower nuclearity systems.

One-pot, exchange-free, room-temperature synthesis of sub-10 nm aqueous, noninteracting, and stable zwitterated iron oxide nanoparticles.

Abstract: Stable aqueous dispersions of superparamagnetic iron oxide nanoparticles were synthesized in one step in the presence of a zwitterionic siloxane as the stabilizing/capping/solubilizing ligand. The hydrodynamic diameter of the particles was tuned by controlling the concentration of zwitterion siloxane, which ultimately yielded monodisperse nanoparticles small enough for renal filtration (<6 nm diameter). The zwitterated nanoparticles were readily dispersed and stable in aqueous media in the pH range 6–9 but exhibited lower magnetization values than nonzwitterated materials due to amorphous content and spin canting, typical for particles of such size. Turbidimetry and light scattering studies revealed no interaction between the particles and proteins, suggesting the materials will circulate well in vivo.

Giant vertical magnetization shift induced by spin canting in a Co/Ca 2 Ru 0.98 Fe 0.02 FeO 4 heterostructure

Abstract: We present a study of exchange bias generated at the interface between a polycrystalline Co film sputtered on a cleavage plane of single-crystal Ca${}_{2}$Ru${}_{0.98}$Fe${}_{0.02}$FeO${}_{4}$. The exchange bias is accompanied by an extremely large vertical magnetization shift that is characterized by 60$%$ of the saturation magnetization in a 70-kOe cooling field. This phenomenon is seldom observed in other heterostructures. The effects of cooling-field amplitude and temperature on the exchange bias indicate that the magnetization shift results from a ferromagnetic contribution of canted moments in Ca${}_{2}$Ru${}_{0.98}$Fe${}_{0.02}$O${}_{4}$. A Type-I training effect is also observed, in which the hysteresis loop shrinks from both sides with cycling of the applied field.

Spin canting phenomenon in cadmium doped cobalt ferrites, CoCd x Fe2−x O 4 ( x = 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), synthesized using sol–gel auto combustion method

Abstract: Synthesis of non-collinear (spin canted) ferrites having the formula, CoCd x Fe2 − x O 4 (x = 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), has been carried out using the sol–gel auto combustion method. The ferrite samples show an interesting magnetic transition from Neel to Yafet–Kittel configuration, as the Cd2 + concentration is increased beyond x = 0·4. The FT–IR spectra confirm the formation of the metal oxide bond as they exhibit two frequency bands in the range of ~595 cm − 1 and ~450 cm − 1, corresponding to the tetrahedral and the octahedral stretching vibrations of the metal oxide, respectively. The structural evolutions of the nanophase investigated using powder X-ray diffraction (XRD) technique show that the average crystallite size is ~ 35 nm. The magnetic studies reveal that the saturation magnetization, M s , increases up to x = 0·4 and decreases when the value of x is >0·4. It is proposed that the incorporation of Cd2 + ion takes place into the tetrahedral sites and up to x = 0·4, Neel’s model is followed. But for x > 0·4, canting of spins occurs, as explained by Yafet–Kittel (Y–K) model. The d.c. resistivity decreases as a function of temperature, indicating semiconducting nature of the ferrites and the positive value of Seebeck coefficient establishes p-type conduction behaviour for all the ferrite samples.

A 2D coordination polymer based on Co3-SBU showing spin-canting ferromagnetic behaviour

Abstract: A 2D MOF with the secondary building unit [Co3(CTC)6(Py)2(OH)2] is synthesized using the sodium salt of a flexible ligand, cis,cis-cyclohexane-1,3,5-tricarboxylate (Na-CTC), and a cobalt trimer ([Co3O(CH3COO)6(Py)3]·ClO4). Structural analysis shows that the complex crystallizes in the monoclinic space group P21/n and forms a 2D framework with channel sizes of 9.0 × 4.2 A2. Magnetic characterization shows spin-canting ferromagnetic behaviour at low temperatures. Frequency dependency for in-phase (χ′M) and out-of-phase (χ′′M) signals at low temperatures is observed from the AC measurements. The gas adsorption behaviour suggests selectivity towards CO2 over N2, and demonstrates enhancement of CO2 uptake (19–33 cm3 g−1) on lowering the temperature (273–195 K).

New two-dimensional Mn(II) metal–organic framework featured spin canting

Abstract: A two-dimensional (2D) complex {[Mn1.5(L)(bpe)1.5]·(bpe)0.5}n (1) (H3L = 3-(2-carboxy-phenoxy)phthalic acid, bpe = 1,2-bis(4-pyridyl)ethene), consisting of manganese(II) chains and bridging bpe ligands, has been synthesized and characterized. The magnetic behavior of 1 can be simulated as a –J1J1J2– alternating chain. Magnetic studies show that this complex magnetic behavior belongs to spin canting and exhibits an unusually high Tc around 40 K. A theoretical study based on DFT-BS calculations provides some insight into the underlying mechanism of the novel magnetic properties.

Ferromagnetic coupling and spin canting behaviour in heterobimetallic ReIVMII/III (M = CoII/III, NiII) species

Abstract: Three novel heterobimetallic Re(IV) compounds of formulae [ReBr4(μ-ox)M(4,7-Cl2phen)2]·CH3CN·CH3NO2 [M = Co(II) (1) and Ni(II) (2)] and [ReBr4(ox)]3[CoIII(5,6-dmphen)3]2·CH3CN·2CH3NO2·4H2O (3) [ox = oxalate, 4,7-Cl2phen = 4,7-dichloro-1,10-phenanthroline and 5,6-dmphen = 5,6-dimethyl-1,10-phenanthroline] have been synthesised and the structures of 1 and 3 determined by single crystal X-ray diffraction. Compound 1 is an oxalato-bridged ReIVCoII heterodinuclear complex where the [ReBr4(ox)]2− unit acts as a bidentate ligand towards the [Co(4,7-Cl2phen)2]2+ entity, the separation between Re(IV) and Co(II) across the oxalate being 5.482(1) A. Compound 3 is an ionic salt whose structure is made up of [ReIVBr4(ox)]2− anions and [CoIII(5,6-dmphen)3]3+cations plus acetonitrile, nitromethane and water as solvent molecules. The magnetic properties of 1–3 were investigated in the temperature range 1.9–300 K. Relatively large ferromagnetic interactions between Re(IV) and M(II) through the bis(bidentate) oxalato occur in 1 and 2 [JReM = +11.0 (1) and +12.2 cm−1 (2), the Hamiltonian being defined as Ĥ = −JReMŜRe·ŜM] which are explained on the basis of orbital symmetry considerations. A behaviour typical of a magnetically diluted Re(IV) complex with a large and positive value of zero-field splitting for the ground level (DRe = +43 cm−1) is observed for 3 in the high temperature range, whereas it exhibits spin canting in the low temperature domain as well as magnetic ordering below ca. 4.8 K.

Low temperature red luminescence of a fluorinated Mn-doped zinc selenite.

Abstract: M2(SeO3)F2 (M = Zn (1), Mn (2)) stoichiometric phases together with the Zn2−xMnx(SeO3)F2 compound doped at various concentrations (x = 0.002–0.2) were synthesized by employing mild hydrothermal conditions. These compounds have been characterized by scanning electron microscopy (SEM), Rietveld refinement of the X-ray powder diffraction patterns, ICP-Q-MS, thermogravimetric and thermodiffractometric analyses, and IR, UV/vis and electron paramagnetic resonance (EPR) spectroscopies. Compounds 1 and 2 crystallize in the orthorhombic Pnma space group with lattice parameters: a = 7.27903(4), b = 10.05232(6) and c = 5.26954(3) A for the zinc species and a = 7.50848(9), b = 10.3501(12) and c = 5.47697(6) A for the manganese phase, with Z = 4. The crystal structures of these compounds are isotypic and are built up from a 3D framework constructed by (010) sheets of [MO3F3] octahedra linked up by [SeO3] building units. Luminescence measurements of Mn2(SeO3)F2 were performed at different temperatures between 10 and 150 K. At 10 K, the emission spectrum consists of a broad band peaked at around 660 nm related to the 4T1g → 6A1g transition in octahedrically coordinated Mn2+. Moreover, the influence of temperatures up to 295 K and the Mn concentration on the luminescent properties of the Zn2−xMnx(SeO3)F2 system were systematically studied. Magnetic measurements of 2 show antiferromagnetic coupling as the major interactions exhibiting a spin canting at low temperature.

Synthesis, structure, and magnetic properties of bithiophene- and terthiophene-linked manganese metal-organic frameworks.

Abstract: A series of metal-organic frameworks (MOFs) containing manganese centers and oligothiophene dicarboxylate linkers have been synthesized: [Mn(3PhT2DC)(DMF)0.45(H2O)2.55·1.55DMF]n (1), [Mn6(3HT2DC)6(DMF)3(H2O)5·xDMF·yH2O]n (2), [Mn(T3DC)(H2O)2]n (3), [Mn(T3DC)(H2O)1.5]n (4), and [Mn(Ph2T3DC)(DMF)2]n (5) (H23PhT2DC = 3,3'-diphenyl-2,2-bithiophene-5,5'-dicarboxylic acid; H23HT2DC= 3,3'-dihexyl-2,2'-bithiophene-5,5'-dicarboxylic acid; H2T3DC = 2,2':5',2″-terthiophene-5,5″-dicarboxylic acid; H2Ph2T3DC = 3',4'-diphenyl-2,2':5',2″-terthiophene-5,5″-dicarboxylic acid, DMF = N,N-dimethylformamide). Compound 1 exists as a 2D sheet, 2-4 are 3D frameworks, and 5 is a 1D chain. Compounds 3 and 4 are isomers, and 3-5 are the first examples of crystallographically characterized terthiophene coordination polymers. In the case of 1, 2, and 5, the extended structure is sensitive to β substitution of the oligothiophene linkers. Compounds 1-3 and 5 show antiferromagnetic behavior with typical values of g and J, and 3 exhibits a spin canting transition at 40 K.

Magnetic Properties of the Spin-1/2 Deformed Kagome Antiferromagnet Edwardsite

Abstract: We prepared a powder sample of edwardsite Cd2Cu3(SO4)2(OH)6·4H2O, which is a new candidate compound for the spin-1/2 kagome antiferromagnet, and studied its magnetic properties by magnetic susceptibility and heat capacity measurements. Edwardsite has a deformed kagome lattice with an average antiferromagnetic interaction of 51 K between nearby spins and shows an antiferromagnetic order accompanied by a small ferromagnetic moment below 4.3 K. The weak ferromagnetism is likely due to spin canting caused by sizable Dzyaloshinsky–Moriya interactions, which may stabilize the long-range magnetic order instead of a spin-liquid state expected for the kagome antiferromagnet.

Cu(I), Co(II) and Fe(II) coordination polymers with pyrazine and benzoate as ligands. Spin crossover, spin canting and metamagnetism phenomena.

Abstract: The isolation and characterization of four coordination polymers obtained by direct reactions of metal ion salts of Cu(II), Co(II) and Fe(II) with pyrazine (pyz) and benzoic/benzoate (Bz) ligands under hydrothermal or hydrothermal microwave conditions are described. The use of copper(II) perchlorate as the starting salt allows us to obtain compounds in a selective way by changing the pH values giving rise to the formation of two 3D-coordination polymers: [Cu(pyz)2]ClO4·pyz (1) and [Cu2(pyz)4](ClO4)2·HBz·H2O (2). In both polymers, 4-connected Cu(I) uninodal coordination networks with significant structural differences between them, due to the templating effect of the solvation molecules and counterions, have been found. However, reactions carried out under similar conditions with MSO4 (M = Co and Fe) led to the isolation of two [M2(μ-Bz)2(μ-pyz)2(Bz)2]·(HBz) isostructural infinite 1D ladder chains (M = Co (3) and M = Fe (4)). These coordination polymers show a spin-canting antiferromagnetism and metamagnetism behaviour for Co(II) and HS ↔ HS/LS ↔ LS spin-crossover phenomena for Fe(II), respectively. The latter compound is the first example of a FeIIO4N2 coordination environment showing this phenomenon.

Cation, Vacancy, and Spin Ordered 15R-Superstructures in Sr(Cr1-xFex)O3-y (0.4 ≤ x ≤ 0.6) Perovskites

Abstract: 15-layer rhombohedral (15R) SrCrO2.8-type superstructures have been discovered in Sr(Cr1-xFex)O3-y perovskites (0.4 ≤ x ≤ 0.6; space group R3m; a ≈ 5.56 and c ≈ 34.6 A). Cr/Fe cations are segregated between layers of tetrahedrally and octahedrally coordinated sites. The 15R-Sr(Cr1-xFex)O3-y materials are semiconducting and order ferrimagnetically below 225–342 K. The magnetic structure of an x = 0.5 sample shows spin canting consistent with a simple spin disorder model. Samples with x ≥ 0.7 have a disordered cubic perovskite structure, and we propose that locally reconstructed (111) planes like those in the 15R materials facilitate oxide ion migration in Cr-based perovskite mixed conductors used in solid oxide fuel cells.